Method for manufacturing a semiconductor display device

ABSTRACT

A method for manufacturing a semiconductor indicating instrument or display device employing a silicon carbide crystal having a first ohmic contact with an n-type region and at least one second ohmic contact with a p-type region. Another region is disposed between the regions of opposite types of conductivity. The silicon carbide crystal also has an additional region with structure defects which are clusters with a concentration of 10 19  cm -3  to 10 22  cm -3 , that region adjoining the second ohmic contact and having a thickness greater than that of the p-type region by at least 0.05 mμ. The method is characterized in that, in order to produce the additional region, the p-type region is bombarded with ions of an inert gas with an ion flow density of 3.1·10 13  ion/cm 2  ·sec to 1.25·10 14  ion/cm 2  ·sec, an ion energy of 10 to 400 keV and an irradiation dose of 1.2·10 16  ion/cm 2  to 6.2·10 17  ion/cm 2 .

This is a division of application Ser. No. 461,718 filed Apr. 17, 1974,now U.S. Pat. No. 3,982,162.

The present invention relates to a method for manufacturingsemiconductor indicating instruments or display devices.

Known at present are different types of semiconductor instruments ordisplay devices intended for the indication and representation ofinformation.

One of the known semiconductor indicating instruments employs a siliconcarbide crystal having a p-n junction, a first ohmic contact with then-type region with a concentration of neutral ions of 1.5·10¹⁸ cm⁻³ to5·10¹⁸ cm⁻³, 7 second ohmic contacts with the p-type region with athickness of 0.1 to 0.3 mμ, producing information to be indicated, and aregion having a thickness of 0.5 to 1.2 mμ and disposed between the n-and p-type regions; there is also an additional region with structuraldefects, the latter region adjoining the second ohmic contacts.

A disadvantage of the above type of semiconductor indicator instrumentis low contrast and poor luminescence efficiency.

Another disadvantage of this semiconductor indicating instrument residesin the presence of a relatively strong conductive coupling between thesecond ohmic contacts, which results in self-coupling of those secondohmic contacts to which no signal is applied at a given moment of time,i.e., an erroneous representation of information is indicated.

Also known at present is a method for manufacturing a semiconductorindicating instrument, in which a p-type region and another regiondisposed between an n-type region and the newly formed p-type region areformed in an n-type silicon-carbide crystal. The formation of the aboveregions is effected by way of introducing an admixture into the siliconcarbide crystal. This is followed by the formation of a first ohmiccontact with the n-type region and at least one second ohmic contactwith the p-type region, after which the p-type region is bombarded withaccelerated ions of an inert gas in order to form an additional regionwith structural defects.

A disadvantage of the above method resides in that the proposedbombardment with argon, nitrogen and oxygen ions does not effectivelyprevent lateral spread of electric current in the silicon carbidecrystal.

It is an object of the present invention to provide a method for makinga semiconductor indicating instrument or display device which rules outself-coupling of the second ohmic contacts and ensures a high contrastand luminescence efficiency.

In accordance with the above and other objects, the present inventionessentially resides in that in a silicon carbide crystal of asemiconductor indicating instrument or display device wherein thecrystal has a first ohmic contact with the n-type region and at leastone second ohmic contact with the p-type region, constituting an areafor information to be indicated, a compensated region with aluminescence activator is disposed between the regions of differenttypes of conductivity, and also having an additional region withstructural defects adjoining the second ohmic contact. The additionalregion has a thickness greater than that of the p-type region by atleast 0.05 mμ, the structural defects therein forming clusters with aconcentration of 10¹⁹ cm⁻³ to 10²² cm⁻³, as will be explained later.

It is recommended that in the proposed device the additional regionconsists of two layers, the first layer directly adjoining the secondohmic contact, having a depth greater than that of the p-type region byat least 0.05 mμ, and also being a dielectric produced on the basis ofsilicon carbide.

The present invention essentially resides in a method for manufacturinga semiconductor indicating instrument or device in which a p-type regionand a region disposed between an n-type region and the newly formedp-type region are formed in an n-type silicon-carbide crystal. Theformation is effected by way of introducing an admixture into thesilicon carbide crystal, which is followed by the formation of a firstohmic contact with the n-type region and at least one second ohmiccontact with the p-type region, after which the p-type region adjoiningthe second ohmic contact is bombarded with accelerated ions of an inertgas in order to form an additional region. The bombardment is effected,in accordance with the invention, at a density of the ion flow of3.1·10¹³ ion/cm² ·sec to 1.25·10¹⁴ ion/cm² ·sec, an ion energy of 10 to400 keV and an irradiation dose of 1.2·10¹⁶ ion/cm² to 6.2·10¹⁷ ion/cm².

It is recommended that in the case of utilizing argon, the ion energy bebetween 20 and 100 keV and the irradiation dose between 6.2·10¹⁵ ion/cm²and 3.1·10¹⁷ ion/cm².

It is expedient that in the case of utilizing krypton, the ion energy bebetween 40 and 200 keV and the irradiation dose between 3.1·10¹⁶ ion/cm²and 6.2·10¹⁶ ion/cm².

It is expedient that in the case of utilizing xenon, the ion energy bebetween 80 and 400 keV and the irradiation dose between 1.2·10¹⁶ ion/cm²and 3.1·10¹⁶ ion/cm².

It is also expedient that the bombardment with ions of an inert gas, inorder to produce an additional two-layer region, be followed bybombardment with accelerated ions of a chemically active element, thisbombardment taking place at an ion flow density of 6.2·10¹³ ion/cm² ·secto 3.1·10¹⁴ ion/cm² ·sec, with an ion energy of 10 to 250 keV and anirradiation dose of 1.2·10¹⁷ ion/cm² to 6.2·10¹⁸ ion/cm².

It is further expedient that in the case of using atomic nitrogen ions,the ion energy be between 10 and 100 keV and the irradiation dosebetween 4·10¹⁷ ion/cm² and 2·10¹⁸ ion/cm².

It is expedient that in the case of using diatomic nitrogen ions the ionenergy be between 20 and 200 keV and the irradiation dose, between2·10¹⁷ ion/cm² and 1·10¹⁸ ion/cm².

It is expedient that in the case of using atomic oxygen ions, the ionenergy be between 20 and 100 keV and the irradiation dose between3.1·10¹⁷ ion/cm² and 1.2·10¹⁸ ion/cm².

It is expedient that in the case of using diatomic oxygen ions, the ionenergy be between 40 and 250 keV and the irradiation dose between1.2·10¹⁷ ion/cm² and 6.2·10¹⁷ ion/cm².

It is expedient that in the case of using carbon ions, the ion energy bebetween 20 and 200 keV and the irradiation dose between 6.2·10¹⁷ ion/cm²and 6.2·10¹⁸ ion/cm².

Other objects and advantages of the present invention will be more fullyunderstood from the following detailed description of specificembodiments thereof when read in conjunction with the accompanyingdrawings, wherein:

FIG. 1 shows the structure of a semiconductor indicating instrument ordisplay device manufactured in accordance with the invention;

FIG. 2 is a section along line 2--2 of FIG. 1;

FIG. 3 shows the structure of a semiconductor indicating instrument witha two-layer additional region, in accordance with the invention; and

FIGS. 4, 5, 6, 7, 8 and 9 illustrate operations of the inventive methodfor manufacturing the semiconductor indicating instruments.

Referring now to the attached drawings, a silicon carbide crystal 1(FIGS. 1 and 2) has a thickness of 350 mμ and includes an n-type region2 (FIG. 2) with a concentration of 3·10¹⁸ cm⁻³ of uncompensated nitrogenatoms, a p-type region 3 with a thickness of 0.2 mμ, containing atoms ofaluminum, and a region 4 with a thickness of 0.6 mμ disposed between theregions 2 and 3 of opposite types of conductivity, the region 4containing boron atoms that serve as a luminescence activator.

Adjoining the n-type region 2 is a first ohmic contact 5. Adjoining thep-type region 3 are 7 second metal ohmic contacts 6, the size and shapethereof determining the topology of light-emitting patches which areadapted to process information to be indicated.

An additional region 7 of silicon carbide lies between the contacts 6,the region 7 having a thickness larger by at least 0.05 mμ than that ofthe p-type region 3. The region 7 includes clusters of radiation defectswith a concentration from 10¹⁹ cm⁻³ to 10²² cm⁻³.

The additional region 7 features high electrical resistivity thatprevents lateral spread of electric current in the silicon carbidecrystal 1 and thus improves contrast and luminescence efficiency.

In accordance with another embodiment of the proposed semiconductorindicating instrument or display device, the additional region 7consists of two layers. A first layer 8 (FIG. 3) adjoins the secondohmic contacts 6, is a dielectric incorporating atoms of silicon,carbon, nitrogen or oxygen, and having a thickness by at least 0.05 mμgreater than that of the p-type region 3, whereas a second layer 9includes structural defects or damages which are of radiation defectswith a concentration of 10¹⁹ cm⁻³ to 10²² cm⁻³.

The proposed method for manufacturing the above semiconductor indicatinginstrument or display device is carried out as follows. Introduced byway of diffusion at a temperature between 2,000° and 2,300° C over aperiod from 10 minutes to 4 hours into the silicon carbide crystal 1(FIG. 4) is an acceptor impurity which is aluminum. The impurity isintroduced to a depth of 0.1 to 0.3 mμ, whereby the p-type region 3(FIG. 5) is formed. Then, by way of diffusion at a temperature between1,920° and 1,980° C and over a period from 1 minute to 10 minutes, oneintroduces boron into the silicon-carbide crystal 1. Boron is introducedto a depth of 0.3 to 1.2 mμ, whereby the region 4 is formed (FIG. 6).

Then the 7 second ohmic contacts 6 (FIG. 7) are applied to the p-typeregion 3, and one first ohmic contact 5 to the n-type region 2, which iseffected by way of deposition of titanium and nickel, the thickness ofthe deposition being 0.05 to 0.1 mμ and 0.5 to 1.0 mμ, respectively.

After that the silicon carbide crystal 1 is bombarded, on the side ofthe 7 second ohmic contacts 6, with accelerated ions of an inert gas atan ion flow density of 3.1·10¹³ ion/cm² ·sec to 1.25·10¹⁴ ion/cm² ·sec,an ion energy of 10 to 400 keV and an irradiation dose of 1.2·10¹⁶ion/cm² to 6.2·10¹⁷ ion/cm² in order to produce the additional region 7(FIG. 8) with structural defects in the form of clusters of radiationdefects with a concentration from 10¹⁹ cm⁻³ to 10²² cm⁻³.

When the neutral gas is neon, the ion energy is to be between 10 and 50keV, and the irradiation dose between 1.2·10¹⁷ ion/cm² and 6.2·10¹⁷ion/cm².

If in this case the thickness of the p-type region 3 is between 0.05 and0.2 mμ, the neon ion energy is to be 10 keV, the ion flow density3.1·10¹³ ion/cm² ·sec, and the irradiation dose 1.2·10¹⁷ ion/cm². If inthe latter case the thickness of the p-type region 3 is between 0.2 and0.5 mμ, the neon ion energy is to be 30 keV, the ion flow density6.2·10¹³ ion/cm² ·sec, and the irradiation dose 3.1·10¹⁷ ion/cm².

If the thickness of the p-type region 3 is greater than 0.5 mμ, the neonion energy is to be 50 keV, the ion flow density 1.25·10¹⁴ ion/cm².sec,and the irradiation dose 6.2·10¹⁷ ion/cm².

When the inert gas consists of ions of argon, krypton and xenon, the ionenergy, ion flow density and irradiation dose are selected in accordancewith Table 1 that will follow, depending upon the thickness of thep-type region 3.

Inert gas ions are introduced into the regions 3 (FIG. 7) and 4; in thecourse of deceleration, they form displacement cascades therein. As aresult, clusters of radiation defects are formed which are quenchers ofelectroluminescence and hooks for free charge carriers.

With the above-indicated bombardment conditions, the thickness of theadditional region 7 (FIG. 8) containing the clusters is greater thanthat of the p-type region 3 by at least 0.05 mμ, the clusterconcentration therein being 10¹⁹ cm⁻³ to 10²² cm⁻³.

In the zone of the second ohmic contacts 6 (FIG. 7) the deceleration ofaccelerated neon ions takes place inside the second ohmic contacts 6, sothat the accelerated neon ions do not reach the surface of the siliconcarbide crystal 1.

According to another embodiment of the proposed semiconductor indicatinginstrument or display device, the above bombardment of the siliconcarbide crystal 1 with accelerated ions of an inert gas on the side ofthe 7 second ohmic contacts 6 is followed by a bombardment withaccelerated ions of chemically active elements which implant into thesilicon carbide and form with the silicon atoms a dielectric compound,whereby the two-layer additional region 7 is formed (FIG. 9). Used forthis purpose are ions of nitrogen, oxygen and carbon. The bombardment iscarried out at an ion flow density of 6.2·10¹³ ion/cm² ·sec to 3.1·10¹⁴ion/cm² ·sec, an ion energy of 10 to 250 keV, and an irradiation dose of1.2·10¹⁷ ion/cm² to 6.2·10¹⁸ ion/cm².

With the use of atomic ions of nitrogen the ion energy is between 10 and100 keV, and the irradiation dose between 4·10¹⁷ ion/cm² and 1·10¹⁸ion/cm².

If the thickness of the p-type region 3 is between 0.05 and 0.2 mμ, theenergy of atomic ions is 10 keV, the ion flow density 6.2·10¹³ ion/cm²·sec, and the irradiation dose 4·10¹⁷ ion/cm².

If the thickness of the p-type region 3 is between 0.2 and 0.5 mμ, theenergy of atomic ions is 40 keV, the ion flow density 1.25·10¹⁴ ion/cm²·sec, and the irradiation dose 1·10¹⁸ ion/cm².

In case the thickness of the p-type region is more than 0.5 mμ, the ionenergy is 100 keV, the ion flow density, 3.1·10¹⁴ ion/cm² ·sec, and theirradiation dose 2·10¹⁸ ion/cm².

In all the above cases, the first layer 8 of the additional region 7 isa dielectric of the silicon nitride type.

In the case of using diatomic ions of nitrogen, the first layer 8 of theadditional region 7 is a dielectric of the silicon nitride type; in thecase of using atomic and diatomic ions of oxygen, the first layer 8 ofthe additional region 7 is a dielectric of the silicon oxide type; inthe case of using atomic ions of carbon, the first layer 8 of theadditional region 7 is a dielectric compound based upon silicon carbidewith an increased carbon content.

In all the above cases, the ion energy, ion flow density and irradiationdose are selected in accordance with Table 2, also to follow, dependingupon the thickness of the p-type region 3.

Accelerated ions of a chemically active element are introduced into thesurface portion of the additional region 7 (FIG. 8), containing theclusters and, interacting with atoms of silicon, form the first layer 8(FIG. 9) of the additional region 7 in the form of a dielectric compoundon the basis of silicon carbide.

The first layer 8 has a thickness which is greater than that of thep-type region 3 by at least 0.05 mμ; hence, the boundary between thep-type region 3 and the region 4 is enveloped by a dielectric insulator,which rules out any direct contact between that boundary and the secondlayer 9 including structural defects in the form of clusters ofradiation defects.

The semiconductor device can form all the numerals from 0 to 9; theluminescence color is yellow.

As a signal is applied to the first ohmic contact 5 (FIG. 2) and some ofthe second ohmic contacts 6, an injection of minority charge carrierstakes place, which is accompanied by their recombination and theproduction of luminescence in the portion of the region 4 disposed abovethe second ohmic contact 6.

The clusters with a concentration of 10¹⁹ - 10²² cm⁻³ contained in theadditional region 7 of the silicon carbide crystal 1 form compensatingcenters which quench electroluminescence in the additional region 7. Dueto the fact that free charge carriers are hooked by the compensatingcenters, the additional region 7 has a high resistance, which rules outeffectively and completely any conductive coupling between the secondohmic contacts 6 and makes for a high contrast and efficiency ofluminescence.

The presence of the first layer 8 (FIG. 3) provides reliable insulationof the boundary between the p-type region 3 and the region 4. Thisreduces leakage currents, as compared to the first embodiment of theproposed semiconductor device, and raises the brightness of luminescencewith low current densities.

The brightness of the devices produced by the proposed method is 100 -350 nit at a current density of 3.5 - 4.5 a/cm². The devices areoperable within a temperature range from -60° to +125° C.

                  Table 1                                                         ______________________________________                                                       Bombardment Conditions with p-type                             Type           Region Thickness                                               of                 0.05 - 0.20                                                                             0.20 - 0.5                                                                            over 0.5                                 Ion  Parameter     mu        mu      mu                                       ______________________________________                                        20.sub.Ne                                                                          Ion Energy, keV                                                                             10        30      50                                            Ion Flow Density,                                                                           3.1 · 10.sup.13                                                                6.2 · 10.sup.13                                                              1.25 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           1.2 · 10.sup.17                                                                3.1 · 10.sup.17                                                               6.2 · 10.sup.17                     ion/cm.sup.2                                                             40.sub.Ar                                                                          Ion Energy, keV                                                                             20        40      100                                           Ion Flow Density,                                                                           3.1 · 10.sup.13                                                                6.2 · 10.sup.13                                                              1.25 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose:                                                             ion/cm.sup.2  --        --      --                                       84.sub.Xe                                                                          Ion Energy, keV                                                                             40        100     200                                           Ion Flow Density,                                                                           3.1 · 10.sup.13                                                                6.2 · 10.sup.13                                                              1.25 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           3.1 · 10.sup.16                                                                4.5 · 10.sup.16                                                               6.2 · 10.sup.16                     ion/cm.sup.2                                                             132.sub.Kr                                                                         Ion Energy, keV                                                                             80        200     400                                           Ion Flow Density,                                                                           3.1 · 10.sup.13                                                                6.2 · 10.sup.13                                                              1.25 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           1.2 · 10.sup.16                                                                1.8 · 10.sup.16                                                               3.1 · 10.sup.16                     ion/cm.sup.2                                                             ______________________________________                                    

                  Table 2                                                         ______________________________________                                        Type           Bombardment Conditions with p-type                             of             Region Thickness                                               Ion  Parameter     0.05- 0.20 mu                                                                            0.20- 0.5 mu                                                                          0.5 mu                                  ______________________________________                                        14.sub.N                                                                           Ion Energy, keV                                                                             10         40      100                                          Ion Flow Density,                                                                           6.2 · 10.sup.13                                                                 1.25 · 10.sup.14                                                             3.1 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           4.10.sup.17                                                                                1 · 10.sup.18                                                               2 · 10.sup.18                      ion/cm.sup.2                                                             14.sub.N.sbsb.2                                                                    Ion Energy, keV                                                                             20         80      200                                          Ion Flow Density,                                                                           6.2 · 10.sup.13                                                                 1.25 · 10.sup.14                                                             3.1 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                             2 · 10.sup.17                                                                  6.2 · 10.sup.17                                                              1 · 10.sup.18                      ion/cm.sup.2                                                             16.sub.O                                                                           Ion Energy, keV                                                                             20         40      100                                          Ion Flow Density,                                                                           6.2 · 10.sup.13                                                                 1.25 · 10.sup.14                                                             3.1 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           3.1 · 10.sup.17                                                                  6.2 · 10.sup.17                                                             1.2 ·  10.sup. 18                   ion/cm.sup.2                                                             16.sub.O.sbsb.2                                                                    Ion Energy, keV                                                                             40         100     250                                          Ion Flow Density,                                                                           6.2 · 10.sup.13                                                                 1.25 · 10.sup.14                                                             3.1 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose,                                                                           1.2 · 10.sup. 17                                                                 3.1 · 10.sup.17                                                             6.2 · 10.sup.18                     ion/cm.sup.2                                                             12.sub.C                                                                           Ion Energy, KeV                                                                             20         40      200                                          Ion Flow Density,                                                                           6.2 · 10.sup. 13                                                                1.25 · 10.sup.14                                                             3.1 · 10.sup.14                     ion/cm.sup.2 · sec                                                   Irradiation Dose                                                                            6.2 · 10.sup.17                                                                  1.2 · 10.sup.17                                                             6.2 · 10.sup.18                     ion/cm.sup.2                                                             ______________________________________                                    

What is claimed is:
 1. A method for manufacturing a semiconductordisplay device, comprising the steps of: forming in an n-typesilicon-carbide crystal a diffused p-type region and a diffused regionwith a luminescence activator disposed between an n-type region and thenewly formed p-type region; the formation being effected by way ofintroducing an impurity into the crystal, followed by the formation of afirst ohmic contact attached to the n-type region, and at least onesecond ohmic contact attached to the p-type region; thereafterbombarding the p-type region with ions of an inert gas in order toproduce an additional region of silicon carbide, incorporating clustersof structural radiation defects with a concentration of 10¹⁹ cm⁻³ to10²² cm⁻³, at an ion-flow density of 3.1·10¹³ ion/cm² ·sec to 1.25·10¹⁴ion/cm² ·sec, an ion energy of 10 to 400 keV, and an irradiation dose of1.2·10¹⁶ ion/cm² to 6.2·10¹⁷ ion/cm².
 2. The method as defined in claim1, wherein neon is used as the inert gas, the ion energy being between10 and 50 keV, and the irradiation dose between 1.2·10¹⁷ ion/cm² and6.2·10¹⁷ ion/cm².
 3. The method as defined in claim 1, wherein argon isused as the inert gas, the ion energy being between 20 and 100 keV, andthe irradiation dose between 6.2·10¹⁶ ion/cm² to 3.1·10¹⁷ ion/cm². 4.The method as defined in claim 1, wherein krypton is used as the inertgas, the ion energy being between 40 and 200 keV, and the irradiationdose between 3.1·10¹⁶ ion/cm² and 6.2·10¹⁶ ion/cm².
 5. The method asdefined in claim 1, wherein xenon is used as the inert gas, the ionenergy being between 80 and 400 keV, and the irradiation dose between1.2·10¹⁶ ion/cm² and 3.1·10¹⁶ ion/cm².
 6. The method as defined in claim1, wherein said bombarding step with ions of the inert gas is followedby bombardment with accelerated ions of a chemically active element atan ion-flow density of 6.2·10¹³ ion/cm² ·sec to 3.1·10¹⁴ ion/cm² ·sec,an ion energy of 10 to 250 keV, and an irradiation dose of 1.2·10¹⁷ion/cm² to 6.2·10¹⁸ ion/cm².
 7. The method as defined in claim 6,whereion ions of nitrogen are used as the active element, the ion energybeing between 10 and 100 keV, and the irradiation dose between 4·10¹⁷ion/cm² and 2·10¹⁸ ion/cm².
 8. The method as defined in claim 6, whereindiatomic ions of nitrogen are used as the active element, the ion energybeing between 20 and 200 keV, and the irradiation dose between 2·10¹⁷ion/cm² and 1·10¹⁸ ion/cm².
 9. The method as defined in claim 6, whereinatomic ions of oxygen are used as the active element, the ion energybeing between 20 and 100 keV, and the irradiation dose between 3.1·10¹⁷ion/cm² and 1.2·10¹⁸ ion/cm².
 10. The method as defined in claim 6,wherein diatomic ions of oxygen are used as the active element, the ionenergy being between 40 and 250 keV, and the irradiation dose between1.2·10¹⁷ ion/cm² and 6.2·10¹⁷ ion/cm².
 11. The method as defined inclaim 6, wherein ions of carbon are used as the active element, the ionenergy being between 20 and 200 keV, and the irradiation dose between6.2·10¹⁷ ion/cm² and 6.2·10¹⁸ ion/cm².